Listening to the BBC World service I heard of this strange feature of Catalan nativity scenes. Its the very necessary inclusion of a Caganer, pronounced Cack'an'ae in the nativity scene. Catalan nativity scenes are more than just the manger but a scene of Bethlehem with a Caganer usually partially hidden behind a bush or tree. Why? it's a person in the act of defecating, with the produce of a bowel movement evident should you have any doubt.
This scatological squatting figure, now plastic, formally pottery as this is no new phenomenon, but dates from the 17th century, is now symbolised in famous faces, not faeces, including the British Queen.
Explanations of origins and meaning are vague, but strongly held, if a caganer is not featured the nativity scene is definitely not complete and not Catalan.
try
http://www.bbc.co.uk/news/world-europe-12059969